It is well known in the art of drilling oil and gas wells, to place stabilizers along the drill string to mechanically stabilize the drill string. In particular, stabilizers are used to maintain a preferred spacing between the axis of the drill string and the side of the wellbore. As such, stabilizers can prevent differential sticking, especially when positioned in the drill string adjacent the drill bit. Moreover, stabilizers can be utilized to increase the stiffness of a drill string, particularly when incorporated as part of the bottom hole assembly (BHA).
Stabilizers can also be used control the direction of drilling of the wellbore, either by maintaining a strait trajectory for the drill bit path or by inducing a deviation in the path of the drill bit.
Typically, stabilizers are comprised of elongated, axial blades extending from the stabilizer body. The blades are either straightor spiral in orientation and integrally formed as part of the body. Such stabilizers are often referred to as “fixed blade” stabilizers. Fixed blade stabilizers have a predetermined diameter and thus, are disposed only to maintain a predetermined offset of the drill string axis from the side of the wellbore.
When a drill string is made up, afixed blade stabilizer having a predetermined diameter is inserted between drill pipe or collar sections and the pipe is tripped into the wellbore. The stabilizer maintains the spacing of the drillstring from the wellbore wall at the predetermined offset distance. To the extent it is desired to alter the offset distance, the fixed blade stabilizer must be tripped out of the wellbore, the drillstring broken and a stabilizer having the preferred diameter inserted into the drillstring.
Another type of stabilizer is the adjustable blade stabilizer. Adjustable blade stabilizers are most often utilized as part of a directional drilling assembly and include stabilizer blades disposed to be moved radially outward by an actuation mechanism, such as a mud driven piston, once the stabilizer is in a desired location downhole. During deployment, the stabilizer blades are in a retracted position in order to minimize the diameter of the stabilizer. Most commonly, the actuation mechanism is actuated by hydraulic flow through the drill string, thereby causing radial extension of the stabilizer blades. Often, the stabilizers retract when hydraulic flow is interrupted or drops below a predetermined pressure.